Relaxation time and molar free energy of activation of polyacrylonitrile

1981 ◽  
Vol 16 (6) ◽  
pp. 1700-1702 ◽  
Author(s):  
Navin Chand
Keyword(s):  
Free Energy ◽  
Relaxation Time ◽  
Energy Of Activation ◽  
Molar Free Energy ◽  
Free Energy Of Activation

Investigations of the Reversion of Vulcanized Rubber under Heat

1952 ◽  
Vol 25 (2) ◽  
pp. 241-250 ◽  
Author(s):  
Uma Shankar
Keyword(s):  
Free Energy ◽  
Hydrogen Sulfide ◽  
Methyl Iodide ◽  
Energy Of Activation ◽  
Cross Linking ◽  
Molar Free Energy ◽  
Vulcanized Rubber ◽  
Free Energy Of Activation ◽  
Equilibrium Swelling ◽  
Free Sulfur

Abstract (1) During reversion of a vulcanizate, the breakdown of cross-linkages, including those of polysulfides, predominates over any simultaneous reformation of cross-linkages. (2) The reverting modulus falls exponentially with time. (3) The calculated molar free energy of activation is 33.3 ± 1.7 kcal., irrespective of the temperature or the atmosphere of cure or the composition of the mix, and is sufficient to rupture an —S—S— bond. (4) The degree of cross-linking, estimated from the equilibrium swelling measurements in benzene, falls during reversion. (5) The exclusion of oxygen during curing does not prevent reversion if the temperature is high enough to supply the energy needed to break up the cross-linkages. (6) During reversion in nitrogen, hydrogen sulfide is freely evolved, and the C/H ratio rises above the value for C5H8. (7) Evidence for the formation and breakdown of polysulfides during reversion is provided by an increase in free sulfur and a decrease in combined sulfur during a given cure, and the methyl iodide reaction of the reverted vulcanizates.

Viscosity of Dimethyl Sulfoxide + 1,4 Dimethylbenzene System

2008 ◽  
Vol 59 (1) ◽  
pp. 45-48
Author(s):  
Oana Ciocirlan ◽  
Olga Iulian
Keyword(s):  
Free Energy ◽  
Dimethyl Sulfoxide ◽  
Atmospheric Pressure ◽  
Entire Range ◽  
Polynomial Equation ◽  
Energy Of Activation ◽  
Excess Gibbs Free Energy ◽  
Experimental Measurements ◽  
Gibbs Energy Of Activation ◽  
Free Energy Of Activation

This paper reports the viscosities measurements for the binary system dimethyl sulfoxide + 1,4-dimethylbenzene over the entire range of mole fraction at 298.15, 303.15, 313.15 and 323.15 K and atmospheric pressure. The experimental viscosities were correlated with the equations of Grunberg-Nissan, Katti-Chaudhri, Hind, Soliman and McAllister; the adjustable binary parameters have been obtained. The excess Gibbs energy of activation of viscous flow (G*E) has been calculated from the experimental measurements and the results were fitted to Redlich-Kister polynomial equation. The obtained negative excess Gibbs free energy of activation and negative Grunberg-Nissan interaction parameter are discussed in structural and interactional terms.

The crystal structure of ethyl-Z-3-amino-2-benzoyl-2-butenoate and measurement of the barrier to E,Z-isomerization

1980 ◽  
Vol 58 (17) ◽  
pp. 1821-1828 ◽  
Author(s):  
Gary D. Fallon ◽  
Bryan M. Gatehouse ◽  
Allan Pring ◽  
Ian D. Rae ◽  
Josephine A. Weigold
Keyword(s):  
Crystal Structure ◽  
Nuclear Magnetic Resonance ◽  
Hydrogen Bond ◽  
Free Energy ◽  
Magnetic Resonance ◽  
Energy Of Activation ◽  
X Ray ◽  
X Ray Crystallography ◽  
Free Energy Of Activation ◽  
Nuclear Magnetic

Ethyl-3-amino-2-benzoyl-2-butenoate crystallizes from pentane as either the E (mp 82–84 °C) or the Z-isomer (mp 95.5–96.5 °C). The E isomer is less stable, and changes spontaneously into the Z, which bas been identified by X-ray crystallography. The structure is characterised by an N–H/ester CO hydrogen bond and a very long C2—C3 bond (1.39 Å). Nuclear magnetic resonance methods have been used to measure the rate of [Formula: see text] isomerization at several temperatures, leading to the estimate that the free energy of activation at 268 K is 56 ± 8 kJ.

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